ASN lookup

Enter an AS number such as AS13335 to see the network behind it: the organisation, its country and the IPv4 and IPv6 prefixes it announces on the internet. Enter an IP address instead to find the ASN that routes it. The data comes from RIPEstat.

An AS number such as AS13335 or 13335, or an IP address such as 1.1.1.1.
ASN lookup Enter an AS number or an IP address above. You get the network's holder, country and the prefixes it announces.

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What you enter is sent to our server, which asks RIPEstat, the RIPE NCC's public routing data service, about it. Nothing is stored or logged; complete answers are kept in memory for 10 minutes.

How the ASN lookup works

The internet is a network of networks. Each one that makes its own routing decisions, such as an internet provider, a hosting company or a large company, is an autonomous system with its own number (ASN), handed out by one of the five regional internet registries. Networks tell each other over BGP which address blocks (prefixes) they can deliver to.

The tool asks RIPEstat, the RIPE NCC's public routing data service, which collects BGP data from hundreds of routers worldwide. It shows who holds the AS number, the country the registry lists, and every prefix the AS announced in the last two weeks that enough routers saw. For an IP address, it first finds the routed prefix the address is in and the AS that announces it.

The holder is the organisation the AS number is registered to. Its prefixes can be used anywhere in the world: a cloud provider announces the same prefix from many data centers (anycast), so the country is where the network is registered, not where every server stands.

Example

Enter 1.1.1.1 and the tool finds that it is in the prefix 1.1.1.0/24, announced by AS13335. AS13335 is held by CLOUDFLARENET - Cloudflare, Inc., registered with ARIN, and announces thousands of IPv4 and IPv6 prefixes. Entering AS13335 or 13335 directly gives the same network.

Questions

What is an ASN?

An autonomous system number identifies one network on the internet that sets its own routing, such as an internet provider, a hosting company or a large company. AS13335 is Cloudflare and AS15169 is Google. Tens of thousands of them are active on the internet.

How do I find the ASN of an IP address?

Enter the IP address in the field above. The tool finds the routed prefix the address is in and the AS that announces it, then shows that AS's details. An address announced by more than one AS lists all of them.

What is the difference between a 16-bit and a 32-bit ASN?

AS numbers were once 16-bit, from 1 to 65,535. When they ran short, 32-bit numbers up to 4,294,967,295 were added (RFC 6793). Both work the same today. A 32-bit number is sometimes written in dotted form, so AS1.10 is AS65546; this tool accepts both.

What are private AS numbers?

64512 to 65534 and 4200000000 to 4294967294 are reserved for private use, like private IP ranges. Networks use them for BGP inside their own setup, for example between a server and its provider, and strip them before routes reach the internet.

How do I get my own ASN?

Apply to your regional internet registry (ARIN, RIPE NCC, APNIC, LACNIC or AFRINIC), directly or through a sponsoring member such as a hosting provider. You usually need your own IP space or plans to connect to at least two other networks. Some VPS providers then let you announce your prefixes over BGP from their servers.